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Technical FAQ: Clamping carbon frames, AXS compatibility

Lennard offers advice about how to secure a carbon frame into a workstand; discusses SRAM AXS drivetrain cross-compatibility; how to re-align rear derailleur hangers.

Dear Lennard,
I’ve gotten a lot of mixed information about how to clamp a carbon frame into a repair stand. I have always used an aluminum seatpost and clamped that. Or, on my bikes with oddly-shaped posts, I’ve used a fork mount stand.

I’ve read a few threads about clamping a carbon bike by the top tube, and it seems to have a lot of support.

Personally, it seems like a bad idea to me, but I’d love your input… Especially if you’ve spoken with some larger manufacturers, Trek, Specialized, etc…
— Taber

Dear Taber,
You’re right; clamping the top tube is a bad idea. There definitely is something way better; this Hirobel clamp is what we use in my shop for clamping carbon bikes.
― Lennard

Dear Lennard,
Can you use any narrow/wide chain with the SRAM force AXS rear derailleur, or am I limited to the SRAM flat chain?
— Mark

Dear Mark,
While you could in theory run another 12-speed chain through that derailleur (like Campagnolo or SRAM Eagle), if you are using a SRAM AXS 12-speed rear cassette, the only chain you can use is the SRAM Flattop 12-speed chain. That’s because the teeth and valleys on the rear AXS road cogs are designed to mate with the larger rollers in the Flattop chain. If you were to run, for example, a Campagnolo or SRAM Eagle 12-speed chain on that cassette, it would skip.

You can read more about the compatibility of SRAM road 12-speed chains, cassettes and chainrings.
― Lennard

SRAM Red eTap AXS

The FlatTop chain used with the AXS ensemble is narrow, providing smooth shifting with the 12-speed set-up launched by SRAM in 2019. Photo: Rob Arnold

Dear Lennard,
I saw your technical FAQ here about mullet drivetrains. I have a bike with the mullet AXS setup and want a second set of wheels with a more road-oriented setup. You mentioned that you had someone with the 10-33 cassette on a second set of wheels.  When they swapped wheelsets, did they have to swap derailleurs too? Would it be possible to do everything with the Eagle derailleur and chain?
— Julien

Dear Julien,
The gravel road disc bike with an AXS drivetrain and two sets of wheels with vastly different cassette sizes that I described, used the same rear derailleur for both setups. There was no need to change the SRAM X01 Eagle AXS 12-speed rear derailleur, because it works with both chains and cassettes. On the X01 Eagle 10-50 12-speed cassette, we used a GX Eagle chain. When the customer switches wheels to the set with a Force AXS 10-33 12-speed cassette, he has to switch to a Force AXS Flattop chain, as its larger rollers match the tooth valleys in the cassette. Due to the much smaller largest cog on the Force cassette, we made the length of the Force chain shorter than the GX Eagle chain. And each time he switches the wheel and chain, he has to make a large adjustment to the derailleur b-screw.

A requirement to do this interchange is a pair of master link pliers like this Park tool or one from Wolf Tooth Components.
― Lennard

More about misaligned derailleur hangers

One can bend rear derailleur hangers back into place, using a hanger alignment tool.Photo: Caley Fretz

Dear Lennard,
I couldn’t help but wonder what you’d do with a rear derailleur hanger that was misaligned? I simply bend them into alignment if they’re investment cast steel types.

With removable aluminum ones I’d do the same, but only after making sure I had a replacement, just-in-case, though I’ve never had one break off.

I’ve always done the same thing with ’em on the front as well, simply bend the whole works (using the derailleur itself as a lever) until the cage lines up correctly.

Can’t say I’ve done this on a Colnago Master, which I assume is steel, but I have never had an issue on the hundreds of steel frames with front braze-on mounts I’ve worked on over the years.

I’ve assembled hundreds of Italian and American lugged steel bikes with braze-on fittings for front derailleurs over the years — never had the “beer-can” effect happen. I suppose a “Conan the Barbarian” type mechanic (and I’ve seen my share) could ruin anything, but I wonder about the strength/integrity of a seat tube and braze-on so easily “beer canned” under normal use?

I do remember something about SLX tubes having their internal ribbing oriented to reinforce this area but whether the tubing was Columbus, Reynolds, True-Temper, Oria or Deddacciai, it was always pretty simple to bolt on the front derailleur securely and then check the alignment in relation to the chainrings and if things didn’t line up just right, gently and carefully pull or push until it was perfect.

But I understand that if someone had responded to the question this way and the result was the “beer-canning” of the guys treasured frame’s seat tube, YOU would get the blame.
—Larry

Dear Larry,
Yes, I align bent rear derailleur hangers, using a hanger alignment tool as I mentioned in a previous column.

I know that you can often get away with tweaking a front derailleur boss, and your method of bending by pulling on the derailleur itself is better for this issue than bending the braze-on alone with a Crescent wrench, because the derailleur cage probably is what is getting bent more than the braze-on or the seat tube. That said, as a framebuilder who used to subsist on doing a lot of repairs on steel frames, I have dealt with seat tubes that were cracked at the front derailleur braze-on. I suspect that bending the braze-on played a role in some, if not all, of those tube failures.

The crack likely wouldn’t happen at the time of the bending; rather, it would develop over time. The area along the braze-on can be weakened by going beyond its yield strength while bending it, making the tube vulnerable to subsequent fatigue failure during normal riding.

Furthermore, there are two kinds of steel front derailleur braze-ons, ones that are stamped out of thick, sheet steel, and ones that are investment cast. The stamped ones have only one tip on the surface that is brazed to the tube; it points toward the back. If you bend back on one of these, you can start peeling the long, front edge away from the tube along a crease in the stamped steel; I have seen this happen.

The Colnago in the photo has an investment-cast front derailleur braze-on. The issue for bending the investment-cast ones is that they are so stiff that I don’t think they would bend before the tube would, and they have so much brazing surface perfectly shaped to mate with the tube that the braze will not give, either. There is a point on either end of the base of the braze-on that can push into the seat tube. If you do bend on one of these braze-ons with a Crescent wrench, you can see the tube flex as the point of the braze-on pushes into it, and this is where my beer-canning comment came from. Certainly, the spiral ribs inside of a Columbus SLX seat tube, if the point is sitting on one of these ribs, can resist this flexing and possible beer-canning of the tube.
― Lennard

Tubeless tires inner layer

Dear Lennard,
The tubeless tires that we manufactured had a butyl layer which made the tire airtight without the need to use a sealant, but today for our tubeless-ready tires, we use a layer of technical polyamide which is also used as reinforcement against puncture, and use of sealant is mandatory to make the tire airtight.
Joël Balez, Hutchinson R&D projects manager


Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn